Microsoft Account Errors

How to Fix Microsoft 365 Guest Username EXT Format Error

Maira Mehtab Sep 20, 2026 868 views

Question details

An administrator needs to remove the #EXT# format from a guest user's name after converting them to a member, but encounters an editing error with a correlation ID.

Product: Microsoft 365
Device & OS: not provided
Scenario: Updating a recently converted guest user's username to a standard company-domain address in the Microsoft 365 Admin Center or Terminal.
Observed behavior: The system rejects the username update, displaying the error message 'We're sorry, the user couldn't be edited' along with a correlation ID, despite no duplicate usernames existing.

Before you start

Ensure you are logged into the Microsoft 365 Admin Center with Global Administrator or User Administrator privileges to perform diagnostic checks and update user identities.

Solution 1

Rule Out Browser Cache and Session Issues

Use a private browsing window to ensure cached credentials or corrupted browser cookies are not causing the update error.

Open a Private Window

Launch your web browser and open a new InPrivate (Edge) or Incognito (Chrome) window to start a clean session.

Access the Admin Center

Navigate to the Microsoft 365 Admin Center and sign in with your administrator credentials.

Attempt the Username Update

Locate the converted guest user and try changing the username to the company-domain address again.

Solution 2Recommended

Check Active Directory Synchronization Status

Verify if the account is cloud-only or synced from an on-premises Active Directory, as synced accounts cannot be directly modified in the cloud.

Solution 3

Collect Logs and Open a Support Request

If the issue persists for cloud-only users, gather diagnostic data and contact Microsoft Support for backend resolution.

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Frequently Asked Questions

Why do Microsoft 365 guest users have an #EXT# in their username?

Microsoft Entra ID (formerly Azure AD) automatically appends #EXT# to the User Principal Name (UPN) of invited guest users to safely distinguish them from internal members within the directory.

Can I edit an Active Directory synced user directly in Microsoft 365?

No. If a user account is synchronized from an on-premises Active Directory environment via Azure AD Connect, all changes to their username or UPN must be made in the local Active Directory and then synced to the cloud.

What is a correlation ID in Microsoft 365?

A correlation ID is a unique identifier generated by Microsoft's servers when an error occurs. Providing this ID to Microsoft Support helps their engineers trace the exact backend logs to determine why the failure happened.

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